Recovery of tungsten, scandium, iron, and manganese values from tungsten bearing material

ABSTRACT

A process is disclosed for recovering tungsten, scandium, iron, and manganese from tungsten bearing material. The process involves digesting the material in sufficient sulfuric acid at a sufficient temperature for a sufficient time in the presence of a reducing agent to form a digestion solution containing the major portion of the scandium, iron, and manganese, and a digestion residue containing the major portion of the tungsten, separating the digestion solution from the digestion residue and extracting essentially all of the scandium from the solution with an organic consisting essentially of an extracting agent which is a dialkyl phosphoric acid which is present in an amount sufficient to extract essentially all of the scandium without extracting appreciable amounts of iron and manganese, and the balance an essentially aromatic solvent. The scandium containing organic is removed from the raffinate and stripped of the scandium with an aqueous ammonium carbonate solution which is separated from the stripped organic. The pH of the raffinate is adjusted to at least about 2 with a base and electrolyzed to remove the major portion of the iron as iron powder, which is separated from the resulting electrolyzed solution which contains the major portion of the manganese.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Pat. Ser. No. 821,932filed Jan. 24, 1986 now U.S. Pat. No. 4,624,703 issued Nov. 25, 1986.

BACKGROUND OF THE INVENTION

This invention relates to a process for recovering tungsten andscandium, values from a tungsten bearing material containing scandium,iron and manganese. More particularly, it relates to a process forrecovering these values from material resulting from the processing oftungsten ores.

In the processing of tungsten ores such as scheelites, wolframites,hubnerites, or mixtures of the same, typically by digesting in basicmedium as sodium hydroxide or sodium carbonate, the calcium, iron, andmanganese present in the ores are precipitated or form an insolublematerial which is separated from the resulting tungstate solution byfiltration. Since the ores vary in composition, this insoluble materialcan also contain elements such as scandium, arsenic, antimony, niobium,and possibly sulfur and phosphorus. Also, because the digestion oftungsten is usually never complete, the residue contains tungsten.

It would be highly desirable to reclaim the tungsten values and othervaluable elements as scandium, iron, and manganese from these residuesfrom both an economic and and environmental standpoint.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention there is provided aprocess for recovering tungsten and scandium from tungsten bearingmaterial containing tungsten, scandium, iron and manganese. The processinvolves digesting the material in an aqueous solution selected from thegroup consisting of an aqueous solution saturated with sulfur dioxideand sulfuric acid with an additional reducing agent, at a sufficienttemperature for a sufficient time to form a digestion solutioncontaining the major portion of the scandium, iron, and manganese, and adigestion residue containing the major portion of the tungsten,separating the digestion solution from the digestion residue andextracting essentially all of the scandium from the solution with anorganic consisting essentially of an extracting agent which is a dialkylphosphoric acid, which is present in an amount sufficient to extractessentially all of the scandium without extracting appreciable amountsof iron and manganese, and the balance an essentially aromatic solvent.The scandium containing organic is removed from the raffinate andstripped of the scandium with an aqueous ammonium carbonate solutionwhich is separated from the stripped organic.

In an additional recovery step which is another aspect of this inventionthe pH of the raffinate is adjusted to at least about 2 with a base andelectrolyzed to remove the major portion of the iron as iron powder,which is separated from the resulting electrolyzed solution whichcontains the major portion of the manganese.

DETAILED DESCRIPTION OF THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above description of some of the aspects of the invention.

The starting tungsten bearing material of this invention can beessentially any such material. However, the preferred material is thetungsten, scandium, iron, and manganese containing residue which resultsin the processing of tungsten ores as scheelites, wolframites,hubnerites, etc., or mixtures thereof by digesting in basic medium as insodium hydroxide or sodium carbonate.

The typical analysis of such a material is as follows in percent byweight: about 22% Fe, about 18% Mn, about 1.5% W, and about 0.06% Sc.

The tungsten bearing material can be first digested in an aqueoussolution saturated with sulfur dioxide at a sufficient temperature for asufficient time to form a digestion solution containing the majorportion of the scandium, iron and manganese and a digestion residuecontaining the major portion of the tungsten. The solution saturatedwith sulfur dioxide is generally prepared by forming an aqueous slurryof the material and bubbling sulfur dioxide gas through the slurry. Thetypical temperatures are from about 80° C. to about 100° C. with fromabout 90° C. to about 95° C. being preferred. The time is typicallyabout 48 hours.

The tungsten bearing material can also be first digested in sufficientsulfuric acid at a sufficient temperature for a sufficient time in thepresence of a reducing agent to form a digestion solution containingessentially all of the scandium, iron, and manganese and a digestionresidue containing essentially all of the tungsten.

Sulfuric acid does not produce a toxic material such as chlorine gaswhich is produced when hydrochloric acid is used as the digesting acid.Also, sulfuric acid is the least expensive acid. For these reasons, itis chosen as the digesting acid.

It is preferred that the tungsten bearing material be added slowing tothe sulfuric acid because the material usually forms carbonates duringstorage.

Digestion temperatures are typically in the range of from about 100° C.to about 140° C. with from about 130° C. to about 140° C. beingpreferred. The total digestion time is in the range of from about 4hours to about 7 hours with from about 5 hours to about 7 hours beingpreferred.

It is preferred that the sulfuric acid concentration be from about 18normal to about 36 normal. Amounts of sulfuric acid will become apparentin the example.

The reducing agent can be hydrogen peroxide (in acid at a pH of belowabout 7), sulfur dioxide which can be bubbled into the digestionmixture, or elemental iron. Elemental iron is preferred. Hydrogenperoxide interferes with the precipitation of iron in the subsequentelectrolysis step and sulfur dioxide is hazardous to the environment.

The preferred digestion procedure is to first digest the material atfrom about 100° C. to about 130° for from about 2 hours to about 3 hoursto allow the iron in the material to be essentially completely digestedto a form which is soluble in the digestion solution. The resultingdigestion mixture is then diluted typically to about twice its volumewith water. The reducing agent, preferably iron as scrap iron typicallyin an amount of from about 7 to about 8 grams per 100 grams of startingmaterial is then added. After about 4 hours of continuous agitation atabout 100° C., the color of the resulting digestion mixture turns alight tan which indicates the dissolution of the major portion of themanganese in the resulting digestion solution.

The digestion solution is then separated from the digestion residue byany standard method such as filtration.

The digestion residue contains essentially all of the tungsten which waspresent in the starting material. It can also contain SiO₂, CaSO₄, andlesser amounts of iron, manganese, and scandium. A typical weightanalysis is about 4.5% Fe, about 0.71% Mn, less than about 0.03% Sc, andfrom about 5 to about 10% W. The tungsten in the residue is now moreconcentrated than it was in the starting material and can now beprocessed by standard methods such as caustic digestion to render it inusable form.

The digestion solution contains typically the major portion of thescandium, iron, and manganese which were present in the startingmaterial. A typical analysis of the digestion solution is from about 23to about 24 g Fe/l, about 16 g Mn/l, from about 0.15 to about 0.23 gW/l, and about 0.04 g Sc/l.

Essentially all of the scandium is extracted from the digestion solutionwith an organic solution consisting essentially of an extracting agentwhich is a dialkyl phosphoric acid which is present in an amountsufficient to extract essentially all of the scandium without extractingappreciable amounts of iron and manganese, and the balance anessentially aromatic solvent. The formula of the dialkyl phosphoric acidis:

    (RO).sub.2 P(O)OH (RO).sub.2 P(O)O.sup.- H.sup.+.

The preferred dialkyl phosphoric acid is di(2-ethylhexyl phosphoricacid, D2EHPA, which is typically supplied by Mobil Corporation. In thiscase one of the alkyl groups, (R) is 2-ethyl hexyl. Basically themechanism of extraction involves an exchange of the available hydrogenof the dialkyl phosphoric acid for the scandium which is in the cationicform. The extracting agent is selective for scandium over iron andmanganese. The concentration of the dialkyl phosphoric acid is criticalbecause at concentrations above the amount needed to extract thescandium, iron and manganese are extracted along with the scandiumresulting in a less efficient separation of scandium from the iron andmanganese. Furthermore, presence of excess amounts of iron and manganesein the organic can cause emulsions which make the extraction stepinoperable.

The amount of dialkyl phosphoric acid in the organic is thereforegoverned by the amount of scandium in the digestion solution. The amountof dialkyl phosphoric acid which is to be needed can be determinedexperimentally by well known methods in solvent extraction technology.In accordance with a preferred emobdiment of this invention, the typicalamount of D2EHPA is from about 2% to about 10% by volume to extract thescandium from typical digestion solutions, with about 2% by volume beingthe especially preferred concentration. More specific values will beapparent in the example.

The preferred essentially aromatic solvent consists essentially of amixture of alkyl benzenes wherein the alkyl benzenes have molecularweights of 120, 134, or 148 and the total number of carbon atoms in thealkyl chains attached to the benzene ring is either 3, 4 or 5. Typicalconstituents include trimethyl benzene, ethyl benzene, dimethylethylbenzene, methyl properly benzene, tetramethyl benzene, diethyl toulene,dimethylisopropyl benzene, and the like. This material is sold byBuffalo Solvents and Chemicals Corporation under the trade name ofSC#150. In the 1972 edition of "Organic Solvents," a trade publicationof Buffalo Solvents and Chemicals Corporation, SC#150 is listed ashaving a boiling point range of from about 188° C. to about 210° C., aflash point of 151° F., and a specific gravity of about 0.891.

The extraction is carried out by conventional liquid-liquid extractiontechniques as by mixing the organic and digestion solution which isreferred to as the aqueous in a conventional mixer-settler apparatus orin a separatory funnel for a period of time which depends factors as thevolume ratio of the organic and aqueous. The resultingscandium-containing organic phase and aqueous phase which is called theraffinate are then allowed to physically disengage after which they areseparated from each other by conventional liquid-liquid separationtechniques such as by drawing the aqueous from the bottom of the settleror separatory funnel.

In actual practice, it is preferred to contact successively one or more,and preferably 3 fresh aliquots of the organic solution with thedigestion solution to remove essentially all of the scandium from thesolution, followed by removing each scandium-containing organic aliquotafter contact with the digestion solution. The organic aliquots can thanbe combined to form 1 scandium-containing organic.

The scandium is then stripped from the scandium-containing organic withan aqueous solution of ammonium carbonate to form a scandium-containingammonium carbonate solution. The ammonium carbonate stripping solutioncontains preferably from about 5% to about 10% by weight of ammoniumcarbonate.

The scandium-containing ammonium carbonate solution is then separatedfrom the resulting stripped organic solution. This can be done byessentially the same technique as described for the extraction step.

In actual practice the same technique can be carried out as for theextraction step. The scandium-containing organic can be contactedsuccessively with fresh aliquots of the stripping solution to insurethat essentially all of the scandium is stripped from the organicfollowed by separation of each aliquot from the organic after eachcontact. The resulting scandium-containing aliquots of strippingsolution can then be combined to form one scandium-containing strippingsolution.

The scandium-containing ammonium carbonate solution can now be processedby standard methods to recover the scandium. This can be done byevaporation of the solution to dryness followed by heating the resultingsolid to about 400° C. to drive off the ammonium carbonate. The residuetypically contains by weight from about 0.5% to about 10% Sc, from about1% to about 10% Mn, and from about 1% to about 10% Fe. The residue canthen be processed by standard methods to render the scandium is usableform. For example, the residue can be upgraded for use in lasers andother electronic applications.

The raffinate from the scandium extraction is processed to recover theiron and manganese. This is done by first adjusting the pH of theraffinate to at least about 2, and preferably from about 2.5 to about3.0 with a base which is preferably ammonium hydroxide. The pH adjustedraffinate is then subjected to an electric current for a sufficient timeto electrolyze it an form iron powder containing the major portion ofthe iron which was in the raffinate and an electrolyzed solutioncontaining the major portion of the manganese. The preferredelectrolyzing conditions are from about 12 to about 24 amps at about 6to about 12 volts for from about 10 to about 12 hours.

Essentially all of the iron is converted to iron powder which can beused as is, for example to make pressed parts.

The iron is then removed from the electrolyzed solution by standardtechniques such as filtration.

The electrolyzed solution is then processed by standard methods torecover the manganese. One method is by adjusting the pH to from about9.0 to about 9.5 with ammonium hydroxide and bubbling air into thesolution for about 4 hours. The manganese precipitates as Mn₃ O₄ and Mn₂O₃.

One example of the use of Mn₃ O₄ and Mn₂ O₃ is in combination with ironto produce ferro manganese for the steel industry.

To more fully illustrate this invention, the following non-limitingexample is presented.

EXAMPLE

About 100 g of dry tungsten bearing material containing in percent byweight about 22% Fe, about 18% Mn, about 1.5% W, and about 0.06% Sc isadded slowly to about 300 cc of about 18N H₂ SO₄. The resulting slurryis digested at about 140° C. for about 2 to 4 hours to digest the iron.The slurry is then diluted to about twice its volume with water andabout 8 grams of scrap iron is added. After about 4 more hours ofcontinued agitation at about 100° C., the color of the slurry changes toa light tan which indicates the dissolution of the major portion of themanganese. The resulting digestion mixture is filtered. The insolublescontain in percent by weight about 4.5% Fe, about 0.71% Mn, less thanabout 0.03% Sc, about 5-10% W, and some SiO₂, and CaSO₄. The resultingfiltrate contains Fe, Mn, and Sc.

The filtrate is contacted three times with a 2% by volume solution ofD2EHPA in SC#150 to extract the scandium. The organic (about 100 cc) isthen stripped three times with about 33 cc aliquots of a 10% weightsolution of ammonium carbonate in water to remove the scandium. Theresulting combined ammonium carbonate strip solution is then evaporatedto dryness and then heated to about 400° C. to drive off the ammoniumcarbonate. The brownish residue contains in percent by weight from about1 to about 10% by weight Sc, from about 1% to about 10% Fe, and fromabout 1% to about 10% Mn.

The raffinate from the extraction of Sc is adjusted to a pH of fromabout 2.5 to about 2.8 with ammonium hydroxide and then electrolyzed atabout 6 to 12 volts with from about 12 to 24 amps. About 16 to 24 hoursare required under these conditions to remove essentially all of the Fefrom the raffinate.

The iron is then separated from the resulting electrolyzed solution byfiltration and the electrolyzed solution is then made basic withammonium hydroxide to a pH of from about 9.0 to about 9.5 and air isbubbled into it for about 4 hours. The manganese is precipitated as Mn₃O₄ and Mn₂ O₃.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed:
 1. A process for recovering tungsten and scandium froma material containing tungsten, scandium, iron and manganese, saidprocess comprising:(a) digesting said material in an aqueous solutionselected from the group consisting of an aqueous solution saturated withsulfur dioxide and sulfuric acid in the presence of a reducing agent ata sufficient temperature and for a sufficient time to form a digestionsolution containing the major portion of said scandium, iron, andmanganese, and a digestion residue containing the major portion of saidtungsten; (b) separating said digestion solution from said digestionresidue; (c) extracting essentially all of said scandium from saiddigestion solution with an organic solution consisting essentially of anextracting agent which is a dialkyl phosphoric acid which is present inan amount sufficient to extract essentially all of the scandium withoutextracting iron and manganese, and the balance an essentially aromaticsolvent; (d) separating the resulting scandium-containing organic fromthe resulting raffinate; (e) stripping the scandium from thescandium-containing organic with an aqueous solution of ammoniumcarbonate to form a scandium-containing ammonium carbonate solution; (f)separating said scandium-containing ammonium carbonate from theresulting stripped organic solution.
 2. A process of claim 1 in whichthe aqueous solution is sulfuric acid of a concentration of from about18 normal to about 36 normal.
 3. A process of claim 1 wherein saidtungsten bearing material is digested in sulfuric acid at from about100° C. to about 140° C. for from about 4 hours to about 7 hours.
 4. Aprocess of claim 1 wherein said reducing agent is iron.
 5. A process ofclaim 1 wherein the extracting agent is di(2-ethylhexyl) phosphoricacid.
 6. A process of claim 5 wherein said aromatic solvent consistsessentially of a mixture of alkyl benzenes wherein the alkyl benzeneshave molecular weights of 120, 134, or 148 and the total number ofcarbon atoms in the alkyl chains attached to the benzene ring are either3, 4, or
 5. 7. A process according to claim 1 containing the followingadditional steps:(a) adjusting the pH of said raffinate to at leastabout 2 with a base; (b) subjecting the resulting pH adjusted raffinateto an electric current for a sufficient time to electrolyze saidraffinate and form iron powder containing the major portion of the ironwhich was in said raffinate and an electrolyzed solution containing themajor portion of the manganese; and (c) separating said iron powder fromsaid electrolyzed solution.
 8. A process of claim 7 wherein saidraffinate is adjusted to a pH of from about 2.5 to about 3.0.
 9. Aprocess of claim 8 wherein the pH is adjusted with ammonium hydroxide.10. A process of claim 10 wherein said raffinated is subjected to anelectric current of from about 12 to about 24 ampheres at from about 6to about 12 volts for about 10 to about 24 hours.